1. Field of the Invention
The invention relates to a control apparatus and method for an internal combustion engine and a fuel property determining apparatus and method.
2. Description of the Related Art
For example, an internal combustion engine is known which can be powered by, as well as gasoline, various other fuels such as alcohol-blended liquid fuel that is obtained by adding alcohol to gasoline. However, because the property of gasoline and the property of such alcohol-blended liquid fuel are different and the concentration of alcohol in alcohol-blended liquid fuel is not always constant, the fuel property may vary upon refueling.
When the fuel property varies, for example, the value of the stoichiometric air-fuel ratio changes. Therefore, in the case where the fuel injection amount is controlled using a feedback correction coefficient based on the output from an air-fuel ratio sensor in the exhaust passage so as to bring the actual air-fuel ratio to the target air-fuel ratio, the average of the feedback correction coefficients indicates the fuel property. In view of this, there is known an internal combustion engine that is controlled in accordance with the fuel property indicated by the average of the feedback correction coefficient (Refer to Japanese patent publication No. JP-A-2006-77683).
In this internal combustion engine, after the property of the fuel in the fuel tank has changed due to refueling of the fuel tank, the value of the feedback correction coefficient gradually changes and then becomes stable at a value corresponding to the property of the fuel. Therefore, when the property of the fuel to be supplied to the engine has significantly varied as a result of refueling of the fuel tank, it takes a long time before the feedback correction coefficient becomes stable. During the period before the feedback correction coefficient becomes stable, the fuel property can not be accurately determined. Therefore, when the engine is restarted after refueling, the engine can not be appropriately controlled based on the fuel property for a while.